VMS Help EXCHANGE, INITIALIZE, Qualifiers, /EXTRA_WORDS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /EXTRA_WORDS=n

    Specifies, for RT-11 volumes, the number of extra words to add
    to each directory entry, in addition to the required seven words.
    The ability to increase the length of directory entries is useful
    for some RT-11 applications. Increasing the size of the directory
    entries reduces the number of entries that fit in each directory
    segment.